1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
Priority is claimed on Japanese Patent Application No. 2008-042560, filed Feb. 25, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
Recently, multilayering has been proposed with the demand for higher-density semiconductor devices. The multilayering includes forming, on a monocrystalline substrate, multiple SOI (silicon on insulator) layers each including an insulating film and a silicon layer formed on the insulating film. Since a circuit is formed in each silicon layer, each silicon layer needs to be formed as a monocrystalline substrate having few defects. Conventionally, contact holes are formed in an insulating film, followed by forming a first monocrystalline layer by epitaxial growth from the monocrystalline substrate in the contact holes. Then, a second monocrystalline layer is further formed over the insulating film and the first monocrystalline layer with the first monocrystalline layer as a seed layer.
PCT International Publication No. WO98-058408, and Japanese Patent, Laid-open Publication Nos. 2003-338542 and S63-172457 disclose epitaxial growth technologies of monocrystalline silicon layers.
FIGS. 32A to 34 are cross-sectional views indicative of process flow illustrating a method of manufacturing a conventional SOI substrate. FIG. 32A is a plane view illustrating a state when a circular contact hole 30 is formed in a silicon oxide film 3. FIG. 32B is a cross-sectional view taken along a line E-E′ shown in FIG. 32A.
As shown in FIGS. 32A and 32B, the contact hole 30 penetrates a silicon nitride film 2 and the silicon oxide film 3 sequentially formed on a monocrystalline silicon substrate 1. A sidewall 4 made of a silicon nitride film is formed on an inner surface 3a of the contact hole 30. The upper surface of the monocrystalline silicon substrate 1 is partially exposed to the contact hole 30.
The contact hole 30 is formed by: sequentially forming the silicon nitride film 2 and the silicon oxide film 3 on the monocrystalline silicon substrate 1; etching the silicon oxide film 3 by lithography and dry etching so that the silicon nitride film 2 is partially exposed; forming a silicon nitride film over the entire surface; and etching the silicon nitride film by dry etching so that the upper surface of the monocrystalline silicon substrate 1 is partially exposed. At this time, the sidewall 4 is formed on the inner surface 3a of the contact hole 30.
Then, a monocrystalline silicon layer is formed in the contact hole 30 by epitaxial growth. In this case, lattice mismatch does not occur between the monocrystalline silicon substrate 1 and the monocrystalline silicon layer. Thereby, a monocrystalline silicon layer 16 having few defects can be formed.
However, the sidewall 4 made of a silicon nitride film is formed on the inner surface 3a, and therefore lattice mismatch occurs between the silicon nitride film and the monocrystalline silicon layer. Accordingly, the monocrystalline silicon layer that has grown in contact with the silicon nitride film includes many defects which spread. Thereby, a monocrystalline silicon layer 17 having many defects is formed.
As a result, the monocrystalline silicon layers formed in the contact hole 30 includes the monocrystalline silicon layer 16 having few defects and the monocrystalline silicon layer 17 having many defects as shown in FIG. 33
Then, a monocrystalline silicon layer 18 covering the silicon oxide film 3 is formed by continuing the epitaxial growth with a portion of the monocrystalline silicon layer 17 protruding from the silicon oxide film 3 as a seed layer. Thereby, the monocrystalline silicon layer 18 is an SOI layer.
However, the monocrystalline silicon layer 18 is formed by the epitaxial growth with the monocrystalline silicon layer 17 having many defects as a seed layer. Therefore, the monocrystalline silicon layer 18 includes many defects and cannot be a SOI layer having few defects.
In the conventional epitaxial growth method, a surface toward which a monocrystalline silicon layer is not to be grown needs to be masked by an insulating film. Since lattice mismatch necessarily occurs between the insulating film and the monocrystalline silicon layer, the grown monocrystalline silicon layer necessarily includes many defects.
When a silicon oxide film is used as an insulating film, lattice mismatch occurs, and therefore the grown monocrystalline silicon layer includes many defects similarly to when a silicon nitride film is used as an insulting film.
When a semiconductor element, such as a transistor, is formed in an SOI layer including a monocrystalline layer having many defects, many problems arise such as that a leakage current (such as a junction leakage) cannot be reduced, degrading the reliability of a semiconductor device.